The output rate of a gas turbine can be a strong function of inlet temperature. However, how hot a gas turbine can be operated at can be limited by metallurgical constraints of the turbine parts and the cooling effectiveness of those parts. To keep parts cool and therefore maximise output, cooling air drawn from the gas turbine compressor can be used to cool parts. This draw-off, however, can represent a direct loss in gas turbine efficiency. It can be desirable to minimise the draw-off by, for example, ensuring optimal use of the cooling air.
A large number of cooling designs have been developed with the objective of providing effective cooling. Known designs use a variety of convection cooling designs including cooling augmentation features and film cooling schemes with impingement cooling arrangements. Convective cooling arrangements additionally may also include cooling augmentation features, which are features that can improve cooling effectiveness by increasing wall surface area and/or creating wall turbulence. Examples of cooling augmentation features can include pins projected from the inside walls of the of the vane, ribs positioned obtusely to the cooling air flow and pedestals, which are a form of pin, projected across the gap between vane pressure side and suction side walls.
An example of a cooling arrangement is provided in U.S. Pat. No. 7,097,418 which discloses an airfoil impingement cooling arrangement. EP 1 221 538 B1 discloses another arrangement that includes an airfoil impingement cooling system utilising impingement tubes contained and partitioned within a plurality of cavities of the airfoil. Further disclosed are chordwise ribs used to direct cooling medium flow in the chordwise direction within these cavities. The foregoing documents are incorporated herein by reference in their entireties.